1. Field
The configuration relates to a controller for an internal combustion engine with a supercharger, the controller allowing an operation at a leaner air-fuel ratio than a theoretical air-fuel ratio.
2. Description of Related Art
Japanese Patent Application Publication No. 2014-181681 (JP 2014-181681 A) below discloses an internal combustion engine that is configured to suction evaporated fuel from a canister via an ejector by using differential pressure between an upstream side and a downstream side of a compressor of a supercharger and to purge the evaporated fuel into the upstream side of the compressor in an intake passage. According to this configuration, even in a supercharging range where intake manifold pressure is higher than atmospheric pressure, the evaporated fuel that is stored in the canister can be purged and processed into the intake passage.
There is a case where the intake manifold pressure becomes higher than exhaust manifold pressure in the internal combustion engine with the supercharger. At this time, in a valve overlapping period in which both of an exhaust valve and an intake valve are opened, scavenging occurs, that is, a phenomenon where intake air is blown from the intake manifold to the exhaust manifold. When scavenging occurs, the evaporated fuel that is purged into the intake passage remains uncombusted and is blown together with the intake air to the exhaust manifold. Meanwhile, a three-way catalyst (in more detail, a start catalyst disposed directly downstream of a turbine) is generally provided in an exhaust passage. Thus, the blown evaporated fuel can be purified by the three-way catalyst.
By the way, when the internal combustion engine is operated at a leaner air-fuel ratio than a theoretical air-fuel ratio, an exhaust gas temperature becomes lower than that when the internal combustion engine is operated at the theoretical air-fuel ratio. When the exhaust gas temperature is decreased, a temperature of the three-way catalyst, which is provided in the exhaust passage, is also decreased. Furthermore, when an operation air-fuel ratio is leaner than the theoretical air-fuel ratio, oxygen concentration in exhaust gas is increased. Thus, the noble metal of the three-way catalyst is more likely to be subjected to oxygen poisoning. In particular, in a situation where scavenging occurs, the intake air directly flows into the three-way catalyst. Thus, the oxygen poisoning of the three-way catalyst is further likely to occur. Because of these reasons, when the operation air-fuel ratio of the internal combustion engine is leaner than the theoretical air-fuel ratio, the evaporated fuel that is blown by scavenging may not sufficiently be purified due to degradation of purification performance of the three-way catalyst.